Fixed socket.detach()

Author: otethal

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/socket/SocketBuiltins.java

@@ -692,7 +692,9 @@ int fileno(PSocket socket) {
     abstract static class SockDetachNode extends PythonUnaryBuiltinNode {
         @Specialization
         int detach(PSocket socket) {
-            return socket.getFileno();
+            int fd = socket.getFileno();
+            socket.setFileno(-1);
+            return fd;
         }
     }